This invention is directed generally to circuit breakers and, more specifically, to a circuit breaker that has a blade assembly in which a torsion spring acts both as a contact pressure point, providing the required pressure to the blade to maintain a closed position, and as a latch, preventing the blade from closing after a short circuit interruption has occurred.
Circuit breakers are used to provide circuit protection for low voltage distribution systems. Electrical circuits or electrical systems are protected by circuit breakers from electrical overcurrent conditions, such as overload conditions as well as low and high level short circuit or fault current conditions.
One component that contributes to the successful interruption of the circuit breaker when undesired overcurrent conditions occur is a blade. The blade is subjected to a resisting force which typically is preset to allow the blade to open only when certain conditions are met, i.e., when the current passing through the circuit breaker is above a particular threshold. This resisting force is generally provided by a blade spring. The blade spring may also be used, generally in combination with some other member such as a pin, to provide a latching mechanism that prevents the blade from reaching a closed position without the knowledge of a circuit breaker operator.
However, one of the disadvantages of the prior art devices is that, generally, more than one component is required to create a successful latching mechanism. For example, a prior art device uses a blade spring-pin combination wherein the spring and the pin work in unison to provide a latch that will retain the blade in its blown-open position. As the blade of that device rotates the pin translates along one arm of the blade spring, and acts as a barrier for the blade when the blade attempts to return to its closed position.
Another disadvantage of prior art devices is that the blade spring requires, in general, another component to secure the blade spring to a blade frame. Similarly, a blade pin on which the blade can freely rotate requires additional components to secure the blade pin in its position.
Another disadvantage of prior art devices is that in order to protect the blade spring complicated blade shields are attached. The blade shields add extra components and extra assembly steps in assembly.
Accordingly, it is an object of this invention to use a blade spring that can perform the latching feature of the blade and that can secure itself to the blade structure without the use of additional components.
It is another object of this invention to integrate a shield into the blade housing that will protect the blade springs from debris caused by arcing.
It is yet another object of this invention to use a blade pin that is self-retaining.
In accordance with a preferred embodiment of the invention, a circuit breaker for interrupting the flow of current upon the detection of excess current or temperature is provided which has a frame having mounted thereon a fixed contact and conductors for establishing an interruptible current flow path through the fixed contact. A blade cross bar is mounted on the frame for pivoting movement about a blade cross bar axis. The blade cross bar has a current conducting blade mounted for pivoting movement thereon about a blade axis which is preferably radially offset from the blade cross bar. The blade has a moveable contact thereon for engaging and disengaging the fixed contact. The blade cross bar has a blade biasing spring for urging the blade to a first pivotal position on the blade cross bar during the open, closed, and tripped operation of the breaker, and for latching the blade in a second pivotal position on the blade cross bar upon the occurrence of a blow-open action of the breaker.
A spring mounting pin is preferably provided on the blade cross bar parallel to and offset from the blade cross bar axis. A spring follower pin is mounted on the blade parallel to and offset from the blade pivot axis. A hook-accommodating opening is formed on the blade cross bar. A blade bias spring is provided which is a coiled torsion spring coiled around the spring mounting pin and having a first end leg extending outwardly and formed into a hook anchored in said hook accommodating opening, and further having a second end leg extending outwardly and cantilevered into contact with the spring follower pin. The second end of this leg is bent away from the spring follower pin to reduce the spring force exerted between the blade cross bar and the blade upon the occurrence of a blown-open action of the circuit breaker. A mounting hole in the blade positioned on the blade axis is preferably provided, together with a blade pivot pin passing through the hole for mounting the blade. The blade pivot pin is generally cylindrical and has a center section of reduced diameter establishing shoulders on the pin on both sides of the hole in the blade, so that upon application of force on the blade by the spring, the blade pivot pin is locked against displacement from the hole. It is further preferred to provide a barrier on the blade cross bar so positioned that upon pivoting movement of the blade cross bar to a tripped, open, or blown-open position, the barrier is interposed between the spring and the fixed contact, thereby protecting the spring from debris generated in the vicinity of the fixed contact.